1. Field of the Invention
This invention relates to a polishing method and an electropolishing apparatus, and more specifically, a polishing method for accurately determining an end point in an electropolishing required for a case of forming embedded wirings by planarization of concave and convex portions of a copper-plated film surface with a process of forming copper interconnections, a polishing method for polishing by alternating the electropolishing with a chemical mechanical polishing repeatedly, and an electropolishing apparatus for accurately determining an electropolishing end point.
2. Description of Related Art
A detection of an end point in a process of electropolishing a copper-plated film used for copper interconnections has been managed on the basis of a polish time.
However, an electropolishing causes a local increase of a solve-out rate of copper by reason that a micro interconnection portion is electropolished centrally with a decreasing area of a remaining copper film portion. Thus, there is a narrow margin of detection of the end point when a determination on the end point is made by a time management, so that the electropolishing still presents problems such as a disappearance of micro interconnections and a presence of macro interconnection remains.
Further, a mere conjecture on a quantity of removed copper from a cumulative value of integrating currents finds difficulty in determining an accurate end point, because of a local resistance change attributable to a concentration of currents, in addition to a fact that a current value in the end point is far smaller than that at a time when a whole surface was covered with copper.
As a result, the following problems occur. That is, (1) a polished surface of the copper film constitutes an unstable surface having a poor surface smoothness, (2) there is provided an insufficient interconnection sectional area attributable to a recessed copper interconnection surface as a result of overpolish of copper filled in a trench interconnection portion, (3) a dishing occurs, (4) an erosion occurs and the like. A local non-uniformity caused by the presence of copper remains, the overpolish of the copper and the like as described above produces short circuit failure and/or open circuit failures of interconnections.
In particular, when the trench interconnection portion is the only portion to be electropolished in the end point, a polished area of a copper film is decreased with a decreasing area of a copper surface from a state of 100% that the entire surface is initially covered with copper up to a pattern density. For this reason, the copper in a micro trench interconnection portion is liable to be electropolished centrally, so that a polish rate of an independent micro interconnection portion is increased in an accelerating manner with an increasing polish rate difference between a macro remaining portion or a wide interconnection portion and the independent micro interconnection portion. In addition, variations of electropolishing conditions depending on an extreme change of an anode current density, as well as a deviation from bright electropolishing conditions, produce a poor surface such as a rough surface.